COMPARATIVE STUDY OF SELECTED TOXIC ELEMENTS IN PROPOLIS AND HONEY

Vol. 55 No. 2 2011 Journal of Apicultural Science 97 COMPARATIVE STUDY OF SELECTED TOXIC ELEMENTS IN PROPOLIS AND HONEY A d a m Roman 1, B e a t a M a d r a s - M a j e w s k a 2, E w a P o p i e l a - P l e b a n 1 1 Department of Environmental Hygiene and Animal Welfare, Wrocław University of Environmental and Life Science, Chełmońskiego 38C, 51-630 Wrocław, Poland, 2 Apiculture Division, Warsaw University of Life Sciences, Nowoursynowska 166, 02-787 Warszawa, Poland e-mail: adam.roman@up.wroc.pl Received 27 July 2011; Accepted 22 November 2011 S u m m a r y The aim of the study was to determine the extent of the bioaccumulation of the toxic elements: Zn, Cu, Pb, As and Cd, in propolis and multiflower honey collected from the Wrocław area. Propolis and honey samples were mineralized using the microwave technique at an elevated pressure in the microprocessor station MD-2000 type made by CEM-USA. Quantitative analysis of toxic elements (As, Cd, Cu, Pb and Zn) was performed by a plasma spectrometry method using a Varian ICP-AES apparatus. The sequence of the accumulation level of the studied elements in both bee products was: Zn>>Cu>Pb>As>Cd. The highest concentrations of trace elements were found in propolis. The average concentrations of the examined elements observed in this product were as follows: zinc - 48.1, copper - 6.95, lead - 5.74, arsenic - 0.66 and cadmium - 0.19 mg. kg -1. Significantly lower concentrations of individual elements were indicated in the multiflower honey used in the experiment. An average concentration of zinc, copper, lead, arsenic and cadmium amounted to 3.58, 1.18, 0.98, 0.11, 0.05 mg. kg -1, respectively. Lead was the most problematic element in honey, because its average content exceeded the maximum acceptable concentration over twofold and the lead level was also exceeded in 85% of the studied honey samples. Statistically significant differences (p 0.01) between consecutive concentrations of elements in propolis and honey were confirmed. Keywords: propolis, honey, trace elements, zinc, copper, lead, arsenic, cadmium, accumulation. INTRODUCTION The development of industry especially chemical, engineering and mining industry, as well as traffic-related pollution contributed to a massive increase in environmental pollution. Similarly, intensive chemicalization of agriculture based on pesticides, fertilizers and disinfectants has induced many negative effects on the environment (Street et al., 2009; Pan et al., 2010). Trace elements like cadmium, copper, lead, zinc and arsenic are widely used in the human economy, therefore they are considered as common environmental pollutants. Even low concentrations of these elements may cause many types of human and animal diseases. Cadmium, arsenic and lead have the strongest toxic properties which can be easily dissolved and decomposed. In the environment, these chemical elements often occur in doses higher than the maximum allowable concentrations and may contribute to the formation of tumors in humans. In the case of copper and zinc, only high concentrations show negative influences on human and animal organisms (Kabata-Pendias and Pendias, 1999). The honeybee (Apis mellifera L.) is 100% dependent on flowering plants. Products gathered by the bee colony are a

98 kind of pooled sample from a large area. The pollutants occurring in a given area can also be accumulated in the raw material collected by bees and in bees themselves (Roman, 2009; 2010). Therefore, bees, honey, propolis, and other bee products can be valuable indicator material in the investigation of environmental contamination (Roman, 1997; Barišic et al., 2002; Erbilir and Erdoğrul, 2005; Bogdanov, 2006). An additional advantage of using bees and their products as indicators of the contamination levels in the environment, is the fact that the hives can be easily moved with bees inside, to the next studied place. Raw material for honey production is obtained by honey bees from the external environment, therefore, the raw material also contains pollutants characteristic for the given environment (Roman, 1997). However, during the processing of raw material for honey purposes, worker bees partially purify it from contaminants. Such contaminants include a portion of heavy metals. That is why there is often a lower level of toxic elements in honey than in the raw material the honey was made of (Jabłoński et al., 1995; Roman and Demeńczuk, 2003). On the other hand, purification does not take place during the processing of the raw materials to propolis. Therefore, the concentration of trace elements reflects the structure of these chemical elements found in a given region (Roman, 1997; Conti and Botrè, 2001). The information concerning the concentration degree of heavy metals in bee products may be found in numerous scientific publications (Crane, 1984; Accorti and Persano-Oddo, 1986; Accorti et al., 1990; Szczęsna et al., 1993; Szczęsna et al., 1999; Frazzoli et al., 2007; Pohl et al., 2009). There is a close correlation between heavy metal accumulation in soil and plants, and heavy metal content in bee products (Jones, 1987; Roman, 1997). The aim of the present research was to determine the accumulation degree of selected toxic elements (Zn, Cu, Pb, As and Cd) in multiflower honey and propolis collected from bee colonies in the industrialized region of the Wrocław area. MATERIAL AND METHODS The research material was made up of multiflower honey and propolis samples. Bee products originated from stationary apiaries situated in the Wrocław area (Silesia Lower Province in Poland). Material was obtained in the period from May to August 2008. The study included 20 apiaries (N=20). Both products were collected from 5 bee colonies in each apiary (propolis - n=5 x 20=100, bee honey - n=5 x 20=100). The individual samples were combined into one pooled propolis and honey sample weighing about 50 and 100 g each, respectively. Samples were representative for the particular apiary. Propolis was collected directly from the hives. The wooden walls and frames were scraped down with a sharp instrument. The propolis was then put into clean plastic containers. Honey was also collected directly from honey combs by cutting off part of the cells and squeezing out the honey. The received samples were homogenized as follows: 1) honey - by carefully mixing, and 2) propolis - by freezing, fragmentation and mixing. From each sample, 1000 mg of material were weighed (within a 0.1 mg precision) and diluted with 20 ml of concentrated, spectrally pure, nitric acid solution produced by Merck company. Next, samples were mineralized using the microwave technique at an elevated pressure in the chip-type MD-2000 station manufactured by CEM-USA. Quantitative analysis of chosen toxic elements such as arsenic, cadmium, copper, lead, and zinc were conducted using a Varian ICP-AES plasma spectrometer with mass detection controlled by P-3202 computer cooperating with Philips Scientific analytical combine (PU-7000 model) and CETAC-5000 AT ultrasonic nebulizer

Vol. 55 No. 2 2011 Journal of Apicultural Science 99 of propolis was 46.6%, which suggests a significant dispersion of the results. The level of zinc in multiflower honey in comparison with propolis was lower. The average amount of zinc was 3.58 mg. kg -1 (Tab. 2). The content of this metal in all honey samples was below the permissible standards for honey, i.e. <15.00 mg. kg -1 and ranged from 0.51 to 7.85 mg. kg -1. Statistically significant differences (p 0.01) between zinc concentration in propolis and honey were observed (Tab. 3). The concentration of copper in propolis was significantly higher in comparison with the concentration found in honey. The maximum content was determined as 15.82 mg. kg -1 whereas the average was 6.95 mg. kg -1 (Tab. 1). The concentration of copper in honey was approximately sixfold lower than in propolis - 1.18 mg. kg -1 (Tab. 2). The maximum content of that metal was far below the acceptable standards (10.00 mg. kg -1 ) and was 2.43 mg. kg -1. Statistical analysis showed significant differences in the copper concentration level among bee products (Tab. 3). Another heavy metal with a high concentration in bee products was lead. Its mean concentration was also the highest in propolis and amounted to 5.74 mg. kg -1 (Tab. 1). Maximum content of lead in propolis was more than threefold higher than the average - 16.86 mg. kg -1. The presence of lead in honey was at an average level of 0.98 mg. kg -1 (Tab. 2). T a b l e 1. Concentration of selected toxic elements in propolis (N=20). (Górecka et al., 2001). The level of detection (LOD) in this method reaches 1 ppb, however the level of quantification (LOQ) was different for individual elements (Tab. 1). All quantitative analysis were conducted in the accredited Chemical Laboratory of Multielemental Analyses in the Institute of Inorganic Technology and Mineral Fertilizers, Wroclaw University of Technology (Poland). The results of the research were elaborated statistically by ANOVA. The mean concentrations of elements, standard deviations and correlations between elements were calculated. The significance of mean differences among elements and bee products in treatments was tested using Student s t-test. The level of significance was taken as p 0.05 and p 0.01. RESULTS The permissible content of toxic elements in honey bee and propolis is regulated by the Polish Standards PN-88/A-77626 Bee honey (1988) and PN-R-78891:1996 Propolis (1998). The Polish Standards are still used to assess the quality of bee products but are not compulsory. The propolis was characterized by the highest concentrations of the studied elements (Tab. 1). The average level of zinc was 48.08 mg. kg -1. In turn, in individual samples zinc ranged from 16.88 to 99.68 mg. kg -1. The variation coefficient of metal accumulation in successive samples Concentration Chemical elements (mg. kg -1 ) Cadmium Copper Lead Zinc Arsenic Minimum 0.069 1.73 0.56 16.88 0.087 Maximum 0.802 9.57 9.94 99.68 1.238 Average 0.194 A 6.95 C 5.74 C 48.08 D 0.657 B SD 0.181 4.049 4.490 22.427 0.380 Variation coefficient (%) 93.3 58.3 78.2 46.6 57.8 LOQ 0.001 0.01 0.01 0.100 0.001 N - number of propolis samples; A, B, C, D - differences between the elements assessed highly significant on a level of p<0.01; SD - standard deviation; LOQ - the level of quantification.

100 This value is more than twofold higher than the permissible standard for honey (0.40 mg. kg -1 ). The maximum level exceeded the standards almost four times and it was 1.90 mg. kg -1. Therefore, this heavy metal should be considered as the most burdensome toxicological pollution of honey. Statistically significant differences (p 0.01) between the level of lead in propolis and in multiflower honey were observed (Tab. 3). The highest amounts of arsenic were found in propolis, where its concentration level averaged 0.657 mg. kg -1. In individual samples arsenic ranged from 0.087 to 1.238 mg. kg -1 (Tab. 1). The average content of this element in honey was below the maximum allowable standards (NDS) and amounted to 0.106 mg. kg -1 (Tab. 2). In turn, it was in the range of 0.027 to 0.344 mg. kg -1 in subsequent samples. The considerable wide range of arsenic contents in honey samples was observed as the variation coefficient amounted to 77.4%. Considering the arsenic concentration in the tested bee products, it must be noted that there are statistically significant differences between the products. Generally, the smallest concentration in the examined bee products was observed for cadmium. As in the case of most of the previous trace elements, the highest concentration of cadmium was noted in propolis (Tab. 1). However, the distribution of the results was very wide (from 0.069 to 0.802 mg. kg -1 ) which was confirmed by a high coefficient of variation which amounted to 93.3%. T a b l e 2. Concentration of selected toxic elements in honey (N=20). Chemical elements (mg. kg -1 ) Concentration Cadmium Copper Lead Zinc Arsenic Minimum 0.019 0.45 0.17 0.51 0.026 Maximum 0.121 2.43 1.90 7.85 0.344 Average 0.052 Aa 1.18 B 0.98 B 3.58 C 0.106 Ab SD 0.029 0.563 0.512 2.178 0.082 Variation coefficient (%) 55.8 47.7 52.2 60.8 77.4 LOQ 0.001 0.01 0.01 0.100 0.001 NSD 0.10 10.00 0.40 15.00 0.20 N - number of honey samples; SD- standard deviation; LOQ - the level of quantification; NDS - maximum acceptable concentration according to Polish Standards PN-88/A-77626 Bee honey ; A, B, C - differences between the elements assessed highly significant on a level of p 0.01; a, b - differences between the elements assessed significant on a level of p 0.05. Significance of differences between propolis and honey. T a b l e 3. Bee product Chemical elements (mg. kg -1 ) Cadmium Copper Lead Zinc Arsenic Propolis Honey Average 0.194 B 6.950 B 5.74 B 48.08 B * 0.657 B SD 0.181 4.049 4.490 22.427 0.380 Average 0.052 A 1.180 A 0.98 A 3.58 A * 0.106 A SD 0.029 0.563 0.512 2.178 0.082 A, B - differences between the products within features assessed highly significant on a level of p<0.01; * - Correlations between concentrations of a chosen element in honey and in propolis statistically significant at p<0.05; SD - standard deviation.

Vol. 55 No. 2 2011 Journal of Apicultural Science 101 T a b l e 4. The values of correlation coefficient (r) between the concentration of each element for individual products (N=100). Couples of elements Bee product Honey Propolis Cadmium - Copper 0.111 0.064 Cadmium - Lead -0.05 0.287 Cadmium - Zinc -0.161-0.086 Cadmium - Arsenic -0.206 0.000 Copper - Lead 0.006-0.026 Copper - Zinc -0.112 0.270 Copper - Arsenic 0.007 0.495* Lead - Zinc 0.046 0.271 Lead - Arsenic 0.058 0.011 Zinc - Arsenic 0.073 0.067 * - Correlations between element concentrations statistically significant at p 0.05; N - the total number of the product samples. Significantly lower levels of cadmium were found in multiflower honey (Tab. 2). Statistically highly significant differences (p 0.01) were demonstrated between the content of cadmium in both tested products (Tab. 3). The research showed that the most problematic toxic element in bee honey was lead, since only lead had a mean concentration which was much higher than the acceptable limits. However, the high concentrations of zinc, lead and arsenic in propolis was alarming. The concentration level order of the studied elements in both bee products was as follows: Zn>>Cu>Pb>As>Cd. Correlations significant at p 0.05 were found only between the content of copper and arsenic in propolis (r=0.495). No significant correlation between the concentrations of particular elements in honey was observed (Tab. 4). DISCUSSION The present research demonstrated that propolis exhibited the highest level of toxic element contamination. The concentration of all researched elements in propolis was many fold higher than in honey. This has been confirmed by other research results, which showed high concentrations of heavy metals in propolis (Alcici, 1997; Szczęsna et al., 1999; Dogan et al., 2006; Cvek et al., 2008). Conti and Botrè (2001) also claimed that propolis is much more contaminated with heavy metals than any other bee products. Our results showed the highest concentration of zinc in propolis. Those values can be considered small, especially since other authors obtained different results. Dogan et al. (2006) observed a much higher content of zinc in propolis from different regions of Turkey and Cvek et al. (2008). In the present study, a very low concentration of zinc in honey was observed, and it did not exceed the acceptable limits (15.00 mg. kg -1 ) (PN Honey bee 1988). Comparable levels of zinc were noted by Conti (2000). Very similar results were also observed by Tuzen et al. (2007) and Yazgan et al. (2006). However, Caroli et al. (2000) found that the quantities of zinc in honey were considerably lower than those obtained in the present study. Przybyłowski and Wilczyńska (2001) on the other hand, obtained a slightly higher content of zinc in honey. Comparable levels of copper in propolis from the Opole area was demonstrated by Roman (1997). In turn, Dogan et al. (2006) received a higher value of this trace element concentration, in propolis

102 from different regions of Turkey. The present study demonstrated that accumulation of copper in honey was much smaller than copper accumulated in propolis. The latter has been confirmed by the studies of other researchers (Fernández- Torres et al., 2005; Yozgan et al., 2006; Tuzen et al., 2007). In comparison with the present study, a slightly lower copper concentration in multiflower honey was obtained by Caroli et al. (2000), Forte et al. (2001) and Stankovska et al. (2008). In turn, Pisani et al. (2008) observed copper concentrations lower than 0.100 mg. kg - 1. Only Roman (1997) showed a higher copper concentration in honey from the region of the Legnica- Głogów Copper District (LGOM). The level of lead was also the highest in propolis. In other studies, Roman (2000) showed the mean level of lead concentration amounted to 18.39 mg. kg -1 in propolis from the Głogów area (copper industry). However, earlier studies from the same region demonstrated that the content of lead ranged from 11.48 to 24.02 mg. kg -1, and in the neighboring region (Rudna) from 6.73 to 17.83 mg. kg -1, on average (Roman, 1997). Similar results were obtained when examining the concentration of lead in propolis from the region of Opole. Thus, it can be concluded that concentration of this metal in propolis was high and relatively stable. Much smaller amounts of lead were found in samples of multiflower honey, however, this amount was still more than twofold higher the maximum allowable concentration (0.40 mg. kg -1 ). A comparable concentration of lead, was observed by Roman (1997) in honey from the Głogów area, and by Sodré et al. (2007) in honey from Brazil. On the other hand, Jones (1987) showed lower levels of lead accumulation in British honey. A very low content of this metal in honey from the suburbs of Rome was found by Conti and Botrè (2001). Similarly, small amounts of lead in honey from Turkey were observed by Tuzen et al. (2007), Yazgan et al. (2006), and also by Przybyłowski and Wilczyńska (2001) in honey from Pomerania (Poland). As in the case of the other elements, the arsenic concentration was significantly higher in propolis in comparison with honey. A very similar level of arsenic was found by Roman (1997) in propolis originating from Opole and LGOM. This is most likely the result of a significant contamination of soils in the areas of metallurgical and chemical industry and extensive urban areas, where the accumulation of arsenic in the soil reaches up to 2500 mg. kg -1 (Kabata-Pendias and Pendias, 1999). The present research demonstrated that the average level of arsenic in honey from the Wrocław area did not exceed the acceptable limit (0.20 mg. kg -1 ). A significantly lower concentration of this element was shown by Caroli et al. (2000). Also, in a similar study conducted by Forte et al. (2001) a very low arsenic concentration in honey was confirmed. In turn, Roman (1997) in earlier studies, showed that the average concentration of arsenic in honey derived from the cement industry region ranged from 0.052 to 0.156 mg. kg -1, and in honey from the copper industry area the level of arsenic was between 0.037 and 0.368 mg. kg -1. This aforementioned value is consistent with the maximum content obtained in the present research. In accordance with the trend observed in the present study, cadmium concentration was significantly higher in propolis compared with honey. In earlier studies conducted by Roman (1997), lower levels of cadmium were observed in propolis originating from the copper industry region, but significantly higher levels of cadmium were found in propolis coming from the cement industry region. Moreover, Roman (2000) noted a higher cadmium content in propolis from the Wałbrzych region. The present research demonstrated that cadmium level was almost four times lower in honey than in propolis. A considerably lower cadmium content in honey originating from Turkey was obtained by Tuzen et al. (2007). Very low concentrations of cadmium were obtained by Caroli et al. (2000).

Vol. 55 No. 2 2011 Journal of Apicultural Science 103 In turn, Przybyłowski and Wilczyńska (2001) reported the mean concentration on the level of 0.015 mg. kg -1 in honeys from Pomerania (Poland). Other authors (Yazgan et al., 2006; Conti and Botrè, 2001; Forte et al., 2001; Frías et al., 2008) also confirmed a very low content of cadmium in honey. Jones (1987) obtained a very large range of cadmium concentration in honey, which was from 0.0003 to 0.30 mg. kg -1. In the present study, no statistically significant correlation between the levels of individual elements in honey were demonstrated, except Cu-As in propolis. In turn, only one relationship at a statistically significant level, between the concentrations of copper and arsenic, was found in propolis. However, Frías et al. (2008) found such a correlation between the content of cadmium and zinc and cadmium and lead in honey harvested in Tenerife. The results of the present research and a review of other authors results allow us to conclude unequivocally that the level of toxic trace element concentrations in propolis and in honey depends on the state of the environmental pollution in the area of the material sampling. Therefore, many authors (Jones, 1987; Leita et al., 1996; Roman, 1997; Przybyłowski and Wilczyńska, 2001; Celli and Maccagnani, 2003; Yazgan et al., 2006; Stankovska et al., 2008; Cvek et al., 2008) consider that bee products, including propolis and honey, can be used as bioindicators of environmental pollution, e.g. with heavy metals. CONCLUSIONS 1. Propolis is a bee product that is much more contaminated by toxic elements than multiflower honey. 2. Propolis and honey can be used as bioindicators to evaluate environmental pollution degrees by determining the level of toxic elements accumulated in these products. 3. In both products (propolis and honey), the sequence of the examined element concentrations was the same: Zn>>Cu>Pb>As>Cd. 4. Lead proved to be the most problematic element in honey. Its average concentration was over twofold and it exceeded maximum acceptable concentration. In 85% of the honey samples used in our experiment, the maximum acceptable concentration was exceeded. 5. The maximum permissible concentration of copper and zinc was not exceeded in any of the honey samples. REFERENCES Accorti M., Guarcini R., Modi G., Persano-Oddo L. (1990) - Urban pollution and honey bees. Apicoltura, 6: 43-55. Accorti M., Persano-Oddo L. (1986) - A monitoring service for the city area: Apincitta. Informatore Agrario, 42: 39-41. Alcici M. F. N. (1997) - Heavy metals in propolis. Proceedings of on International Conference on Bee products. Properties, Applications, and Apitherapy. May 26-30. Tel Aviv, Israel 1996. Plenum Press, New York and London, 231-238. Barišic D., Bromenshenk J. J., Keziæ N., Vertaènik A. (2002) - The role of honey bees in environmental monitoring in Croatia. Honey Bees: Estimating the Environmental Impact of Chemicals, 160-185. Bogdanov S. (2006) - Contaminants of bee products. Apidologie, 37: 1-18. Caroli S., Forte G., Alessandrelli M., Cresti R., Spagnoli M., D'ilio S., Pauwels J., Kramer G. N. (2000) - A pilot study for the production of a certified reference material for trace elements in honey. Microchem J., 67: 227-233. Celli G., Maccagnani B. (2003) - Honey bees as bioindicators of environmental pollution. B. Insectol., 56: 137-139. Conti M. E. (2000) - Lazio region (Central Italy) honeys: A survey of mineral content and typical quality parameters. Food Control, 11(6): 459-463.

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106 Badania porównawcze zawartości wybranych pierwiastków o właściwościach toksycznych w propolisie i miodzie Roman A., M a d r a s - M a j e w s k a B., P o p i e l a - P l e b a n E. S t r e s z c z e n i e Celem badań było określenie stopnia bioakumulacji wybranych pierwiastków o właściwościach toksycznych (Zn, Cu, Pb, As i Cd) w miodzie wielokwiatowym i propolisie, pozyskiwanych w rejonie Wrocławia. Próbki propolisu i miodu zmineralizowano techniką mikrofalową pod zwiększonym ciśnieniem w mikroprocesorowej stacji typu MD-2000 produkcji CEM-USA. Analizę ilościową pierwiastków (As, Cd, Cu, Pb i Zn) wykonano metodą spektrometrii plazmowej z wykorzystaniem aparatu Varian ICP-AES. W badanych próbkach propolisu i miodu wykazano obecność pierwiastków o właściwościach toksycznych. Kolejność wielkości kumulacji badanych pierwiastków w obu produktach pszczelich była następująca: Zn>>Cu>Pb>As>Cd. Najwyższe stężenia pierwiastków śladowych stwierdzono w propolisie. Średnie ich zawartości w tym produkcie wynosiły: cynku - 48,1; miedzi - 6,95; ołowiu - 5,74; arsenu - 0,66 i kadmu - 0,19 mg. kg -1. W miodzie wielokwiatowym wykazano znacznie niższe stężenia poszczególnych pierwiastków. Średnia koncentracja cynku wynosiła 3,58; miedzi - 1,18; ołowiu - 0,98; arsenu - 0,11 i kadmu - 0,05 mg. kg -1. Najbardziej problematycznym pierwiastkiem w miodzie okazał się ołów, gdyż jego średnia zawartość ponad 2-krotnie przekroczyła najwyższe dopuszczalne stężenie, które także było przekroczone w 85% próbek tego produktu. Stwierdzono statystycznie wysoko istotne różnice (p 0,01) między zawartością poszczególnych pierwiastków w propolisie i miodzie. Słowa kluczowe: propolis, miód, metale ciężkie, cynk, miedź, ołów, arsen, kadm, akumulacja.